Power supply controller

Abstract

A power supply controller used in a DC/DC converter includes a feedback control unit that generates a pulse-shaped PWM signal having a first level that is one of a high level and a low level and a second level that is the other of the high level and the low level, on the basis of a feedback voltage based on an output voltage of the DC/DC converter; a low voltage detection unit that detects a low voltage of the feedback voltage; and a selection unit that chooses, as a chosen clock signal, a first clock signal having a high duty when the low voltage is not detected by the low voltage detection unit, and chooses a second clock signal having a low duty when the low voltage is detected by the low voltage detection unit. The feedback control unit includes a reset signal generation unit that generates a pulse-shaped reset signal having the first level and the second level, based on the feedback voltage, and a PWM signal generation unit that generates the PWM signal at the first level during a period that is an overlap between a period during which the reset signal is at the first level and a period during which the chosen clock signal is at the first level.

What is claimed is: 
     
       1. A power supply controller used in a direct to direct converter, the power supply controller comprising:
 a feedback control unit that generates a pulse-shaped pulse width modulation signal having a first level that is one of a high level and a low level and a second level that is an other of the high level and the low level, on a basis of a feedback voltage based on an output voltage of the direct to direct converter; 
 a low voltage detection unit that detects a low voltage of the feedback voltage; and 
 a selection unit that chooses, as a chosen clock signal, a first clock signal having a high duty when the low voltage is not detected by the low voltage detection unit, and chooses a second clock signal having a low duty when the low voltage is detected by the low voltage detection unit, wherein 
 the feedback control unit includes
 a reset signal generation unit that generates a pulse-shaped reset signal having the first level and the second level, based on the feedback voltage, and 
 a pulse width modulation signal generation unit that generates the pulse width modulation signal at the first level during a period that is an overlap between a period during which the reset signal is at the first level and a period during which the chosen clock signal is at the first level. 
 
 
     
     
       2. The power supply controller according to  claim 1 , wherein
 the pulse width modulation signal generation unit is an AND circuit into which the reset signal and the chosen clock signal are input. 
 
     
     
       3. The power supply controller according to  claim 1 , wherein
 the reset signal generation unit includes
 an error amplifier to which the feedback voltage and a reference voltage are input, 
 a slope generation unit that generates a slope signal, and 
 a pulse width modulation comparator to which an error signal output from the error amplifier and the slope signal are input. 
 
 
     
     
       4. The power supply controller according to  claim 3 , further comprising:
 a soft start unit that raises the reference voltage at startup, wherein 
 the selection unit ignores a detection result from the low voltage detection unit until a signal indicating completion of a soft start is output from the soft start unit. 
 
     
     
       5. The power supply controller according to  claim 1 , wherein
 the low voltage detection unit includes
 a resistor with one end connected to a terminal to which a power supply voltage is applied, and 
 a negative-channel metal oxide semiconductor transistor including a drain connected to an other end of the resistor, a source connected to a terminal to which a ground potential is applied, and a gate to which a voltage based on the output voltage is applied. 
 
 
     
     
       6. The power supply controller according to  claim 1 , wherein
 the low voltage detection unit has a comparator in which a voltage based on the output voltage and a threshold voltage are input. 
 
     
     
       7. The power supply controller according to  claim 1 , wherein
 in a case where the low voltage is detected by the low voltage detection unit and a level of the first clock signal chosen at that time is the first level, the selection unit maintains a choice of the first clock signal while the first level is maintained, and the selection unit switches to a choice of the second clock signal when the first clock signal is switched to the second level. 
 
     
     
       8. The power supply controller according to  claim 1 , further comprising:
 an external terminal to which the output voltage is applied; and 
 a voltage dividing resistor that divides a terminal voltage of the external terminal to generate the feedback voltage. 
 
     
     
       9. The power supply controller according to  claim 1 , further comprising:
 a first external terminal to which the feedback voltage is applied; and 
 a second external terminal to which a ground potential is applied and that is arranged near the first external terminal. 
 
     
     
       10. A direct to direct converter comprising:
 the power supply controller according to  claim 1 ; and 
 a transistor that is switched based on a pulse width modulation signal generated by the power supply controller.